Engineering & Mining Journal

AUG 2017

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MINE DEVELOPMENT
32 E&MJ • AUGUST 2017 www.e-mj.com
Technological advances are increasing
the real-time data available to block
cave operations. A system of magnet-
ic beacons and readers first tested in
2007 and trialed in a diamond mine in
2014 have reportedly proven capable of
tracking cave propagation and ore flow in
real time. Separately, a system of RFID
chips and readers that was upgraded
in 2015 enables heightened draw con-
trol and material movement monitoring.
Both are claimed to nix costs by enabling
tight planning, controlling dilution and
reducing operator error. And both are
now being pitched as proven technology
available today.
Tracking Cave Propagation
Developed by CRCMining, Elexon Mining
and Rio Tinto, Cave Tracker places rug-
ged magnetic beacons into holes drilled
into rock of strategic interest, usually
above the extraction level. The beacons
travel with the caved muck toward the ex-
traction level. That movement is tracked
with detectors located in and around the
mine. Thus, cave propagation can be cap-
tured in real time, empowering miners
with critical data.
The proof of concept was conducted at
Northparkes copper and gold mine, then
owned by Rio Tinto. A prototype system
was then trialed at Rio Tinto's Argyle un-
derground diamond mine in Australia in
2014. As of last year, it was slated for de-
ployment to Rio's Oyu Tolgoi copper mine
in Mongolia. Also last year it nabbed El-
exon a semifinalist slot in the Australian
Technologies Competition. It is currently
being deployed to Newcrest's Cadia East
gold mine in New South Wales. After
three years of trials and tests, the system,
which is intended to work in conjunction
with other in-situ Elexon products, gives
miners a glimpse of what was previously
invisible: real-time ore flow, Simon Stef-
fen, business manager, Elexon Mining,
said. "The data captured so far has shown
effects that were never actually 'seen' be-
fore," he said. "For example, rat holing
was clearly identifiable."
Seeing into rock presents a formidable
challenge as Wi-Fi and most radio waves
will not penetrate through deep rock. Low
frequency magnetic signals, however, will.
Cave Tracker's beacons employ bat-
tery-powered spinning magnets that
generate a magnetic field. The batteries
have an up to 10-year operating life,
depending on how often the magnet is
spun. At Argyle, for example, the bea-
cons are set to transmit every three
days. "The background magnetic field of
the Earth has no effect on the system's
operation," Steffen said. "For calculat-
ing the Beacon's distance, only magnet-
ic signals very close to the beacon's fre-
quency will be considered. Other signals
are ignored. Magnetic noise in the bea-
con's frequency spectrum can affect the
reading, but most of the noise is filtered
out by algorithms."
Larger beacons allow bigger magnets
to be used, generating stronger signals.
A 135-millimeter (mm)-diameter beacon
has a proven transmission range of 200
meters (m). The 76-mm beacon can talk
to a receiver 150 m away. "We are cur-
rently working on increasing the range
by improving our signal processing algo-
rithms," Steffen said. "Testing thus far
has yielded promising results."
Placement of the beacons is deter-
mined by the type of flow effect that is
desired to be monitored, as well as the
access constraints. For example, bea-
cons placed at the mine boundaries can
reveal if the cave is propagating into un-
desired areas. Beacons placed around
fault boundaries can detect if the cave
has propagated through the fault, and
Block Cave Ops Benefit From
Real-time Data
Proven monitoring systems help underground miners envision the previously
unforeseeable, forge plans, streamline processes and cut costs
By Jesse Morton, Technical Writer
Rio Tinto's Oyu Tolgoi copper mine was slated to deploy Cave Tracker after the system was tested at two of the
company's other mines. Above, drilling before concreting at Oyu Tolgoi. (Photo: Rio Tinto)